1. Field of the Invention
The present invention relates to an organic semiconductor device comprising an organic semiconductor layer made of an organic compound having a marked characteristic of carrier mobility.
2. Description of the Related Art
An inorganic semiconductor, e.g., silicon plays a major role in semiconductor devices such as diodes, and transistors that perform switching and amplifying functions necessary for signal processing, because such devices require multiple performances such as a high carrier mobility, a low dark current, a low driving voltage, and a complicated device structure and the like.
In the field of organic semiconductors, organic electroluminescent devices utilizing the photoelectric conversion characteristics thereof are under development. Furthermore, when an electric field is applied on an organic semiconductor thin-film, a carrier density is increased. Accordingly, when a pair of electrodes is disposed on an organic semiconductor thin-film, an electric current is flowed therebetween. For example, provided that a source electrode and a drain electrode are disposed on an organic semiconductor thin-film and a gate electrode is disposed therebetween so as to apply a voltage across a thickness direction of the thin-film, a switching over the electric current that flows in a direction of the organic semiconductor thin-film can be achieved. Accordingly, organic transistors are also under study, and the organic semiconductors are being utilized in the technology such as information transfer, processing, recording and display that utilize electric signals and control, at a junction interface (metal-organic semiconductor, organic semiconductor-organic semiconductor), carriers (electrons and holes) in the organic semiconductor.
FIGS. 1 and 2 show examples of bottom contact type and top contact type structures of an organic MOS-FET that uses an organic semiconductor thin-film. The organic MOS-FET is provided on a substrate 10 with gate electrode 14, gate insulating film 12, source electrode 11 and drain electrode 15, and organic semiconductor layer 13. As the gate electrode 14, Ni, Cr and the like are used; as the gate insulating film 12, inorganic materials such as oxides or nitrides of metals such as SiO2 and SiN and resins such as PMMA; and as the organic semiconductor layer 13, pentacene and the like. Furthermore, for the source electrode 11 and the drain electrode 15, a single layer film of Pd, Au and the like is used.
However, when a current flows from a source electrode through an organic semiconductor layer to a drain electrode, at the respective interfaces, potential barriers are generated owing to differences between work functions of the source electrode and the drain electrode and an ionization potential of the organic semiconductor layer. As a result, a higher driving voltage is required.